1. Field of the Invention
The present invention relates to an improved corona discharge device for an electrophotographic recording apparatus or the like, and more particularly to a corona generating apparatus that suppresses corona wire vibrations during operation.
2. Discussion of the Art
Corona discharge devices are widely used in various industrial fields such as electrophotographic machines, printing machines, paper manufacturing machines or the like, and are used for charging or in some instances, neutralizing charges. The corona discharge device used for these purposes generally comprises at least one corona discharge electrode in the form of a fine metal wire held taut between connectors or standoffs with a minimum of slack. The gap between the corona wire and the surface of the photoconductive material is generally small for the sake of efficiency. However, as the length of the discharge wire is increased, the tendency to vibrate also increases. In the past, this vibration was believed to have been caused by electrostatic attraction and mechanical vibration. In any event, corona wire vibration results in spark discharge, wire fatigue and nonuniform charging of the photoconductive material. Such spark discharge or short circuiting could result in the breakage of the corona discharge electrode and damage to material being charged.
U.S. Pat. No. 3,656,021 addressed this problem of corona wire vibration by providing means intermediate the corona discharge electrode and a counter electrode for preventing vibration of the corona discharge electrode as a result of electrostatic forces. This is accomplished by having a vibration suppression member positioned between the corona discharge electrode and the counter electrode and substantially parallel thereto, for preventing transverse vibration of said corona discharge electrode as a result of the electrostatic force.
This reference has expressed doubt as to the precise theory and physical mechanism causing the mechanical instability of the corona discharge wires. The explanation as to how and why vibration of the corona wires is suppressed when the insulated vibration suppression members are positioned between the corona discharge electrode and the counter electrode is based on electrostatic forces. The teaching of the patent is more than adequate to allow a person skilled in the art to construct the apparatus as described and realize a significant improvement in corona wire vibration suppression. However, using the theory of operation advanced, it would be difficult for one to extrapolate on the theory of operation in an effort to develop an apparatus.
It has been found that use of insulating materials especially of an organic nature have a tendency to decompose readily in the harsh environment that exists in a corona discharge apparatus and would therefore require routine inspection and replacement.
European Patent Application No. 0 144 236 discloses a corona generating device which comprises a plurality of parallel coronode wires supported between insulating end block assemblies. The coronode wires, made for example, of tungsten oxide are closely spaced e.g., less than 0.2 inches apart such that, when energized, each wire is within the electrostatic fringe field of the adjacent wire. Because the adjacent wires are within the fringe field of each other, one has a tendency to suppress the high output of the other and thereby provide more uniform charge along the length of the corona generating device. The patent states that the spacing of the two wires is absolutely critical in that they must be within the fringe fields generated by each other. The patent advances the proposition that since the two parallel wires provide intersecting fringe fields, a point on one wire opposite a point on the other wire has a tendency to suppress the high output of the other wire. Furthermore, the wires should be parallel to each other to optimize this suppressing effect by each wire on the other wire.